Methods and systems for the rapid detection of concealed objects

Abstract

The present invention provides for an improved scanning process having microwave arrays comprised of microwave transmitters in radiographic alignment with microwave receivers. The microwave array emits controllably directed microwave radiation toward an object under inspection. The object under inspection absorbs radiation in a manner dependent upon its metal content. The microwave radiation absorption can be used to generate a measurement of metal content. The measurement, in turn, can be used to calculate at least a portion of the volume and shape of the object under inspection. The measurement can be compared to a plurality of predefined threats. The microwave screening system can be used in combination with other screening technologies, such as NQR-based screening, X-ray transmission based screening, X-ray scattered based screening, or Computed Tomography based screening.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S) [0001] This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10 / 662,778, filed on Sep. 15, 2003.FIELD OF THE INVENTION [0002] The present invention relates generally to a microwave imaging system that is compatible with X-ray and Nuclear Quadrupole Resonance (NQR) based methods and systems for detection of concealed threats, and threat resolution, and more specifically to improved methods and systems, using dual stage scanning to process luggage for faster inspection with reduced false alarm rate. BACKGROUND OF THE INVENTION [0003] Conventional X-ray systems produce radiographic projection images, which are then interpreted by an operator. These radiographs are often difficult to interpret because objects are superimposed. A trained operator must study and interpret each image to render an opinion on whether or not a target of interest, a threat, is present. With a large number of such radiographs to be in...

AI Technical Summary

Benefits of technology

[0015] One object of the present invention is to provide for an improved scanning process having a first stage to pre-select the locations of potential threats and a second stage to accurately identify the nature of the threat. The improved scanning process increases throughput by limiting the detailed inspection to a small fraction of the total bag volume, and it decreases the frequency of false alarms by applying threat specific analysis.

[0016] Another object of the invention is to provide for improved processing techniques performed in association with various scanning systems. The improved processing techniques enable the substantially automated detection of threats and decrease the dependence on operator skill and performance.

[0020] Yet another object of the present invention is to provide a system that is compact and compatible with being built into the structures typical for housing NQR equipment and X-ray or CT equipment.

[0022] A still further object of the present invention is to provide a system that uses an appropriate frequency of operation such that penetration is sufficient for the detection and imaging of objects within typical packages and bags but with a minimal amount of inaccuracies being introduced due to items with high dielectric loss being present within a bag.

Problems solved by technology

These radiographs are often difficult to interpret because objects are superimposed.

With a large number of such radiographs to be interpreted, and with the implied requirement to keep the number of false alarms low, operator fatigue and distraction can compromise detection performance.

However, the dual-energy method does not readily allow for the calculation of the actual atomic number of the concealed ‘threat’ itself, but rather yields only an average atomic number that represents the mix of the various items falling within the X-ray beam path, as the contents of an actual luggage is composed of different items and rarely conveniently separated.

Thus dual-energy analysis is often confounded.

Even if the atomic number of an item could be measured, the precision of this measurement would be compromised by X-ray photon noise to the extent that many innocuous items would show the “same” atomic number as many threat substances, and therefore the atomic number in principle cannot serve as a sufficiently specific classifier for threat versus no threat.

However, conventional CT systems take considerable time to perform multiple scans, to capture data, and to reconstruct the images.

The throughput of CT systems is generally low.

Coupled with the size and expense of CT systems this limitation has hindered CT use in applications such as baggage inspection where baggage throughput is an important concern.

In addition, CT alarms on critical mass and density of a threat, but such properties are not unique to explosives.

CT based systems suffer from high false alarm rate.

Each of the prior art systems and methods, however, suffer from low processing rates because the scatter interaction cross sections are relatively small and the exposure times required to obtain useful diffraction spectra are long, in the range of seconds and minutes.

However, the use of CT scanning is still inefficient, not threat specific, and does not allow for rapid scanning of objects.

The disclosed system does not, however, address critical problems that arise in the course of applying a scatter probe to a selected suspicious region, including the accurate identification of a suspicious region, correction of detected data, and the nature of processing algorithms used.

One potential weakness of the technique is that, with carefully designed electromagnetic shielding, the materials which it is being used to detect can be rendered undetectable.

This potential problem is mitigated by the fact that such shielding consists of conductive (typically metal) volumes that must completely encapsulate the item to be detected.

However, the presence of a conductive loop around luggage means that the simplest forms of inductive metal detector would have limited performance.

Images